The present invention relates to a method and an apparatus for controlling turbine efficiency in a turbo unit provided on an internal combustion engine.
Turbochargers are well known and widely used with combustion engines for purpose of increasing power output, decreasing fuel consumption and emissions, and compensating for air density loss at high altitudes. Generally, turbochargers supply an increased charge air supply for the combustion process than can otherwise be induced through natural aspiration by utilizing exhaust gas energy to drive an air compressor. This increased air supply allows more fuel to be burned, thereby increasing power and output not otherwise obtainable from an engine having a given cylinder displacement under natural aspiration conditions. Variable geometry turbochargers (VGTs) allow the intake airflow to be optimized over a range of engine speeds. This may be accomplished by changing the angle of the inlet guide vanes on the turbine stator. An optimal position for the inlet guide vanes is determined from a combination of desired torque response, fuel economy, and emission requirement.
EGR systems are used to reduce NOx emissions by increasing the dilution fraction in the intake manifold. EGR is typically accomplished with an EGR valve that connects the intake manifold with the exhaust manifold.
In the cylinders, the recirculated exhaust gas acts as an inert gas, thus lowering the flame and in-cylinder gas temperature and, hence, decreasing the formation of NOx. On the other hand, the recirculated exhaust gas displaces fresh air and reduces the air-to-fuel ratio of the in-cylinder mixture.
On an EGR engine with a variable geometry turbine (VGT) airflow and EGR flow are controlled by the VGT position and the EGR valve. The EGR drive pressure is dependent on turbo efficiency and exhaust temperature. At high turbo efficiencies and/or high exhaust temperatures the EGR drive pressure will be insufficient and large EGR valve areas in combination with small VGT positions have to be used to increase the boost pressure and by that reduce the exhaust temperature and finally drive an adequate amount of EGR. Increasing the boost pressure also normally decreases turbo efficiency which also helps give EGR drive pressure.
This means that, if the turbo efficiency is too high, the boost pressure and other limits on the engine, e.g. turbo speed, max cylinder pressure, compressor temperature, will be too high when the VGT position is decreased to achieve sufficient EGR drive pressure.
To create enough EGR drive pressure the turbo and/or engine are today matched or modified for lower effective turbo efficiency in a way that none of the limits are exceeded in any engine operating point. A consequence of this is a fuel and emission penalty due to increased gas exchange losses and lower lambda in areas where the limits are not reached which may be a problem. The EGR control range will also be limited and sets a limit to the maximum power/torque achievable from the engine which also may be a problem.
It is desirable therefore to overcome the above mentioned problems with gas exchange losses and limited EGR range for a turbo unit.
According to a first aspect of the invention it is provided a method of controlling turbine efficiency in a turbo unit for an internal combustion engine, comprising the steps of: providing a flow of gas in an area upstream a turbine rotor at a direction different to the flow of exhaust gases in the same area, regulating said flow by a valve, controlling said valve from a control unit having at least boost pressure and/or EGR flow as input parameters.
An advantage of an aspect of the present invention is that it enables optimal use of turbo efficiency during a wide operating range.
Another advantage of an aspect of the present invention is that it gives increased controllability of the engine, e.g., turbo speed, compressor temperature, peak cylinder pressure, reduces fuel consumption and increases maximum reachable power/torque from the engine.
In another example embodiment according to an aspect of the present invention it further comprises the step of providing in said area a plurality of outlets for said flow of gas.
An advantage of this embodiment is that it may further increase the controllability of the engine.
In still another example embodiment according to an aspect of the present invention it further comprising the step of providing an on-off valve in each of said outlets.
An advantage of this embodiment is that simple on-off valves arranged in a plurality of outlets may result in a fine adjustment of the flow provided in said area, i.e. by opening one or more of the valves one may regulate the flow in small increments.
In still another example embodiment it further comprising the step of providing a variable valve in each of said outlets.
An advantage of this embodiment is that not only adding another flow by opening another outlet one may also adjust the flow from one single outlet as such, i.e., a further fine adjustment of the flow of gas into the area is possible which in turn may further increase the controllability of the engine.
In still another example embodiment it further comprising the step of providing said valve outside a turbo unit housing.
An advantage of this embodiment is that it is an inexpensive and simple solution which can be applied to existing turbo units.
In still another example embodiment of an aspect of the present invention it further comprising the step of integrating said valve in a turbo unit housing.
An advantage of this embodiment is that it gives a compact turbo unit which may be used in cases where space is limited.
In still another example embodiment of an aspect of the present invention it further comprising the step of providing said flow of gases from a volute of the turbo unit.
An advantage of this embodiment is that it may be a compact solution.
In still another example embodiment of an aspect of the present invention it further comprising the step of providing said flow of gases from an exhaust gas manifold.
An advantage of this embodiment is that the piping from the exhaust manifold to the turbo unit may be short and simple.
In still another example embodiment according to an aspect of the present invention it further comprising the step of providing said flow of gases from an outlet downstream of a compressor of said turbo unit or from an external compressor tank.
An advantage of this embodiment is that it gives sufficient flow of gas at the same time as it may cool down the turbo unit since such flow of gas has a substantially lower temperature than the exhaust gases.
According to a second aspect of the invention it is provided a system for controlling turbine efficiency in a turbo unit for an internal combustion engine comprising at least one outlet arranged in a turbine scroll outlet for providing a flow of gas in a direction different to the direction of exhaust gases in said turbine scroll outlet; a valve arranged between a source for providing a flow of gas and said outlet in said turbine scroll outlet for regulating the flow of the gas; and a control unit for controlling said valve where said control unit has at least boost pressure and/or EGR flow as input parameters.
According to a third aspect of the invention it is provided a vehicle comprising a system for controlling turbine efficiency in a turbo unit for an internal combustion engine comprising at least one outlet arranged in a turbine scroll outlet for providing a flow of gas in a direction different to the direction of exhaust gases in said turbine scroll outlet; a valve arranged between a source for providing a flow of gas and said outlet in said turbine scroll outlet for regulating the flow of the gas; and a control unit for controlling said valve where said control unit has at least boost pressure and/or EGR flow as input parameters.